Rafting alien biota
g.read at niwa.cri.nz
Sun Apr 28 22:19:58 EST 2002
Annelida members may have seen the publicity surrrounding a short note in
Nature last week by David Barnes (1a) on a side effect of increased plastic
debris in the oceans. He says "I ESTIMATE that rubbish of human origin has
roughly doubled the propagation of fauna in the subtropics and more than
tripled it at high (>50 deg) latitudes ...". This becomes in the press release
used in newspapers (1b) that D.B. has "FOUND THAT" floating rubbish has
almost doubled the spread of alien species. Never mind - he has a valid
point, though the item is somewhat short on detail of the species being
transported. One wonders what NEW species are being transported that
haven't been transported by the same mechanism of drift debris, on the
same currents for eons.
However, to balance this I'd like to mention algal rafting, which he rather
ignores. Smith's recent observations (2) lead to claims that in the zone
between Hobart Tasmania and subantarctic Macquarie Island "over 70
million [algal] rafts [are] afloat at any one time, 20 million of which support a
holdfast, the habitat supporting the highest faunal diversity in attached kelp
plants". That's practically a conveyor belt supply (coming towards New
Zealand by the way). It may not only be important to coastal faunas. Parker &
Tunnicliffe (3) suggest that seamounts can be colonised this way. The only
caveat is how long algal rafts can last afloat - Hobday's California Bight paper
(4) suggests about 100 days.
Barnes, D. K. A. 2002. Biodiversity: Invasions by marine life on plastic debris
[Brief Communication]. Nature 416:808 - 809.
Smith, S. D. A. 2002. Kelp rafts in the Southern Ocean. Global Ecology
and Biogeography 11(1):67-69.
Parker, T., & V. Tunnicliffe. 1994. Dispersal Strategies of the Biota on an
Oceanic Seamount - Implications for Ecology and Biogeography.
Biological Bulletin 187(3):336-345.
Hobday, A. J. 2000. Age of drifting Macrocystis pyrifera (L.) C. Agardh rafts in
the Southern California Bight. Journal Of Experimental Marine Biology And
Geoff Read <g.read at niwa.cri.nz>
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